1. Field of the Invention
The present invention relates to a semiconductor device constructed by providing a bump electrode above an electrode pad and a manufacturing method of the same.
2. Description of the Related Art
With a demand for miniaturization and higher performance of an electronic device, higher performance, higher integration, and higher-density mounting of a semiconductor device which is mounted on the electronic device are also demanded.
Therefore, as one way of satisfying the demand for higher-density mounting, so-called bare chip mounting is attracting attention as a mounting form of a semiconductor element (semiconductor chip).
In this bare chip mounting, as a way of connecting an electrode of a semiconductor element and an electrode wiring in a substrate on which the semiconductor element is mounted, so-called face down mounting (flip chip mounting), in which the semiconductor element is mounted on the substrate by providing a bump electrode on a principal surface of a semiconductor chip and connecting the bump electrode to the electrode of the substrate, tends to be used.
When a semiconductor device including the above bump electrode is manufactured, zinc (Zn) is precipitated on an electrode pad, for example, made of aluminum-silicon (Al—Si) by an electroless plating method, and then a nickel (Ni) layer is formed by the electroless plating method with the zinc (Zn) as a catalyst, thereby forming a bump foundation layer.
Subsequently, after a gold (Au) layer is formed so as to cover the nickel layer, the bump electrode is formed using solder or the like as a material on the nickel layer (for example, see Patent Document 1).
[Patent Document 1] Japanese Patent No. 3615206
However, if a conventionally used electrode pad (Si: 1 wt %) made of aluminum-silicon (Al—Si) is used as the electrode pad when the bump electrode is formed by the above conventional art, there is a large possibility that the adhesion of the bump electrode to the electrode pad is not sufficient, which causes detachment of the bump electrode.
Usually, in a so-called shear teat to test the adhesion strength of the bump electrode, as shown in FIG. 10A, the test is performed by bringing a shear tool 111 into contact with a bump electrode 105 formed above the surface of an electrode pad 103 with a foundation layer 104 made of nickel (Ni) therebetween, the electrode pad 103 being provided above a semiconductor substrate 101 with an insulating layer 102 therebetween.
Namely, the sharp-edged shear tool 111 is used, and by moving this shear tool 111 with respect to the bump electrode 105 in a direction parallel to the surface of the semiconductor substrate 101 and bringing it into contact with the bump electrode 105, lateral pressure is applied to the bump electrode 105.
Incidentally, in this figure, numeral 106 denotes a passivation layer made of silicon nitride, polyimide, or the like, and numeral 106a denotes an opening (window) formed in the passivation layer 106.
If the bump electrode 105 is firmly connected to the electrode pad 103, as shown in FIG. 10B, even where the shear tool 111 is brought into contact therewith, the bump electrode 105 is not detached from the electrode pad 103, and the bump electrode 105 stays without its portion of contact with the shear tool 111 being separated and removed.
However, when the adhesion between the electrode pad 103 and the bump electrode 105 is not sufficient, as shown in FIG. 10C, detachment occurs between the electrode pad 103 and the foundation layer 104 due to pressing force of the shear tool 111 to the bump electrode 105, and consequently the bump electrode 105 together with the foundation layer 104 is detached from the electrode pad 103.
As just described, the adhesion between the electrode pad 103 made of aluminum-silicon (Al—Si) and the foundation layer 104 is low, and therefore it is difficult to provide the bump electrode 105 with high adhesion to the electrode pad 103.
The inventor has found that one of the causes of contact between the electrode pad 103 and the foundation layer 104 without sufficient adhesion is the form of zinc (Zn), which acts as a catalyst in the above nickel plating, when it is formed on the electrode pad 103.
Namely, the zinc (Zn) which acts as the catalyst when the foundation layer 104 is formed has low adhesion to the electrode pad 103 made of aluminum-silicon (Al—Si) described above, and hence, as shown in FIG. 11A, a region where zinc (Zn) 107 does not exist occurs on the surface of the electrode pad 103.
The zinc (Zn) 107 is deposited by the electroless plating method such as a double zincate method using a bath containing the zinc, but it is difficult for the bath containing the zinc to come into uniform contact with the surface of the electrode pad 103, so that nonuniform density or one-sided distribution occurs in precipitation/deposition of the zinc (Zn).
This one-sided precipitation of the zinc (Zn) 107 also causes one-sided formation of the foundation layer 104 made of nickel (Ni), and as shown in FIG. 11B, a region S where the foundation layer 104 does not exist occurs on the surface of the electrode pad 103.
Due to the above occurrence of the region where the foundation layer 104 does not exist, as shown in FIG. 1C, the bump electrode 105 is formed across both the foundation layer 104 formed one-sidedly on the electrode pad 103 and a surface-exposed portion of the electrode pad 103, and thereby a portion where the bump electrode 105 comes into direct contact with the electrode pad 103 occurs.
In such a connection structure, not only the adhesion between the electrode pad 103 and the foundation layer 104 further deteriorates, but also a solder component contained in the bump electrode 105 is diffused into the electrode pad 103, which significantly impairs the reliability of the semiconductor device.